The invention concerns a method for priming a fuel metering device for a two-stroke engine comprising at least one piston arranged in a combustion chamber that drives by means of a connecting rod a crankshaft that is rotatably supported in a crankcase, comprising a fuel pump that sucks in fuel from a fuel tank and conveys it to a metering valve that opens into a metering chamber at alternating operating pressure, and comprising a control unit for calculating and controlling the timing for the metering valve for the purpose of metering a fuel quantity corresponding to a load situation of the internal combustion engine.
The invention also relates to a fuel metering device for an internal combustion engine comprising at least one piston arranged in a combustion chamber that drives by means of a connecting rod a crankshaft that is rotatably supported in a crankcase, comprising a fuel pump that sucks in fuel from a fuel tank and conveys it to a metering valve that opens into a metering chamber at alternating operating pressure, and comprising a control unit for calculating and controlling the timing for the metering element for the purpose of metering a fuel quantity corresponding to a load situation of the internal combustion engine.
Fuel metering devices in the form of injection devices are known. For disturbance-free function it must be ensured that the system is free of air. In particular in low-pressure injection systems or in low-pressure fuel supply systems air inclusions cause significant disruptions, in particular when fuel pumps are used that cannot convey air bubbles on their own.
In case of hand-held power tools such as motor chainsaws, trimmers, cut-off machines or the like, two-stroke engines are used as a drive means whose fuel metering devices comprise a fuel pump that is configured as a diaphragm pump and is driven by the fluctuating crankcase pressure of the internal combustion engine. When air bubbles have formed in the pump chamber of the diaphragm pump, the conveying quantity is greatly limited so that particularly when starting an internal combustion engine significant starting problems may be caused. Therefore, so-called purgers are proposed that are operated like a hand pump and must be actuated by the user in order to prime the fuel system. Such hand pumps—purgers—must be additionally mounted and connected to the fuel system. Only once sufficient fuel is present in the pump chamber of the diaphragm pump, its conveying action begins wherein a low-pressure level up to approximately 1 bar is reached.